Problem: What is the greatest common factor of $20$ and $50$ ? Another way to say this is: $\operatorname{gcf}(20, 50) = {?}$
Solution: The greatest common factor is the largest number that is a factor of both $20$ and $50$ The factors of $20$ are $1$ $2$ $4$ $5$ $10$ , and $20$ The factors of $50$ are $1$ $2$ $5$ $10$ $25$ , and $50$ Thus, the greatest common factor of $20$ and $50$ is $10$. $\operatorname{gcf}(20, 50) = 10$